1. Field of the Invention
The present invention relates generally to the fields of electrophotography and hard copy apparatus and, more specifically, to the control of printing and fixing alphanumeric text and images on print media using automatic sensing devices, feedback, and digital control techniques in a laser hard copy apparatus.
2. Description of Related Art
Basically, in electrophotographyxe2x80x94the basic technology behind laser printing such as with Hewlett-Packard Company""s HP(trademark) LaserJet(trademark) productsxe2x80x94a latent image on a charged surface area of a photoconductor is developed, by application of an electroscopic toner to the area. The developed image is transferred to a hard copy medium. Both wet toner chemicals and dry toner powders are known to be used to develop an image using heat fusible toner particles. The image is then fixed, that is, fused to the print medium. (For ease of explanation, the word paper will be used as an exemplary print medium hereinafter; however, as will be recognized by a person skilled in the art, the invention described herein is applicable to all forms of hard copy media such as papers, card stock, transparencies, envelopes, and the like; the word image, or sometimes print depending on the context, is used as a generic term for all alphanumeric text, graphics, photographs, and the like; no limitation on the scope of the invention is intended nor should any be implied.)
In its basic aspects, a laser printing engine 124, shown schematically in FIG. 6 (Prior Art), applies a charge with a scorotron charger 136 to a moving photoconductive insulating surface area of a photoconductor, or photoreceptor, 126. The surface area is exposed to a pattern of light 138, 140. A latent image of the pattern is formed on the charged surface which is then developed by application of electroscopic toner 128, 130, 132, 134 (in this example, color toner) to the photoconductive material. The developed image is transferred to a hard copy medium 152 using a transfer drum 148 with a transfer corona charge unit 150 and transferred to the medium 152 by using another transfer corona unit 154. The image bearing medium 152 is then passed to the fuser 160 subsystem where the toner is fused, or fixed. The photoconductive material insulating surface is then erased 146, cleaned 142, 144, and reused for the next image. This basic construct is used in a variety of state of the art products such as computer printers and plotters, copiers and hard copy scanners, facsimile machines, multifunctional peripherals, and the like (referred to generically hereinafter as printers).
In addition to visual perception of print quality, the effectiveness or reliability of the electrophotographic process is determined in part by how well the toner image stays fixed on the media after the media exits the printing operations. Having an effective temperature in the fuser subsystem is vital to ensuring optimized image quality and achievable print. Too low of a fusing temperature can result in toner which is not properly fixed to the print media; a low strength bond between the toner and the media can cause toner to break from the media with a low degree of mechanical stress. Too high of a fusing temperature can result in melted toner adhering to the surface of the fixing device and offsetting the toner from the correct location on the print media. Either case results in undesirable print defects, often referred to as xe2x80x9cartifacts.xe2x80x9d Variables that determine the effectiveness of the fusing process include (1) paper parameters (the major parameters including surface roughness, thickness, moisture content, chemical composition, base weight, and size), (2) environmental parameters (the major parameters including temperature and humidity of the ambient air), and (3) fuser assembly operational parameters (the major parameters including temperature, pressure, nip size, surface properties of roller, paper speed, and fuser electrical bias).
Another factor in the determination of final print quality will be the bias voltages used in various components of the printer subsystems, e.g., the transfer voltage on the image transfer roller, the charges on various electrostatic charge/discharge elements, and the like as would be known to a person skilled in the art.
In many commercially available systems, many of these parameters are neither sensed nor controlled. The solution to their individual and possibly cumulative negative effect on print quality is to over-design the system to cover worst case scenarios. For example, a fixed fuser temperature is often used, set for a xe2x80x9ctypical mediaxe2x80x9d for which the printer is compatible. However, fixed fuser temperatures cannot accommodate media types that require more heat to properly fuse the toner to the special media; fixed fuser temperatures may be too high for special media; media types requiring lower fuser temperatures may be damaged, e.g., wrinkled, by the relatively high heat of a fixed temperature fuser.
Other conventional arrangements provide user controls for manually adjusting operational parameters. Typically, such manual adjustments are made after print problems are already occurring; thus, print monitoring is required for prompt attention.
In co-pending applications, the common assignee has provided some specific, advanced solutions:
U.S. Pat. No. 6,011,939, based on Ser. No. 09/126,628, filed by co-inventor Martin on Jul. 30,1998, addresses SENSING PRINT MEDIA SIZE TO TEMPERATURE CONTROL A MULTI-HEATING ELEMENT FIXING DEVICE by relating media size to given print data;
U.S. Pat. Appl. Ser. No. 09/348,650, filed by co-inventor Martin et al., on Jul. 6,1999, addresses IMAGE FORMING DEVICES, FUSING ASSEMBLIES AND METHODS OF FORMING AN IMAGE by monitoring media qualitative characteristics to adjust fusing parameters;
U.S. Pat. Appl. Ser. No. 09/354,638, filed by co-inventor Martin et al., on Jul. 16,1999 addresses AUTOMATIC FUSER TEMPERATURE CONTROL; sensed media vibrations are related to print media type and fuser temperature selected using the measured sympathetic response;
U.S. Pat. Appl. Ser. No. 09/384,716, filed by co-inventor Martin et al., on Aug. 26,1999, addresses issues with respect to METHOD AND APPARATUS FOR DETECTING IMAGE MEDIUM SURFACE DEFECTS IN AN IMAGING SYSTEM by monitoring the fuser subsystem pressure roller and heated roller surface conditions; and
U.S. Pat. Appl. Ser. No. 09/430,356, filed by co-inventor Martin, on Oct. 28, 1999, addresses issues with respect to FIXING DEVICE CONTROL BASED UPON MEDIA TEXTURE MEASUREMENT using optical sensing; rough media requires a higher fuser temperature than smooth media.
One type of planar type fuser is shown in assignee""s patent for a THERMAL TRANSFER APPARATUS FOR FUSING PRINT DYE ON A MEDIA, U.S. Pat. No. 5,541,636, file Jun. 2, 1994 by G.B. Ingram.
There is a need for an overall system approach to detecting the necessary properties of the paper and ambient environment as the paper is being processed and using feedback information to control the printing operational parameters, automatically optimizing in real-time the processes for each media type supported by the device.
The present invention relates to a method and apparatus for controlling the fuser assembly operation by substantially continuously feeding sensor information, viz., signals indicative of fuser operating parameters, ambient environment conditions, and current copy paper characteristics and performance, to a control circuit. As media is fed into the hard copy apparatus from an input supply and throughout the printing process, a variety of detection devices determine media properties, ambient environmental conditions, and current fuser assembly operating conditions such that feedback signals are sent to the controller and real time adjustments made to fuser assembly operating conditions appropriate to optimize the fixing of an image on the next sheet as it passes through. Moreover, output print characteristic detectors can be used to provide direct print quality feedback to the controller.
In its basic aspects, the present invention provides a print fusing system, including: print fuser having a plurality of individually controllable heaters; a controller connected to said heaters; and connected to said controller, at least one sensor for ambient environmental conditions, at least one sensor for media parameters, at least one sensor for current print fuser system conditions, such that signals from each said sensor to said controller are provided to said controller for adjusting fusing system conditions to optimal for the next media sheet passing therethrough.
In another aspect, the present invention provides a hard copy apparatus, having mechanisms for applying toner to a print media sheet in a predetermined pattern and a controller for printing and media transport subsystems of the apparatus, including: connected to the controller, a toner fuser device having a plurality of individually controllable heaters for thermally fixing the toner to the sheet, at least one sensor for ambient environmental conditions, at least one sensor for media parameters, at least one sensor for current fusing system conditions, wherein signals from each said sensor are provided to said controller for adjusting fusing system conditions to optimal for the print media sheet passing therethrough.
In another aspect, the present invention provides a method for hard copy print fusing using automated sensing devices in a hard copy apparatus, including the steps of: monitoring for a set of predetermined characteristics a sheet of print media transported from an input of the hard copy apparatus to the output of the hard copy apparatus; producing a set of signals indicative of the predetermined characteristics; post-print deposition operations, running a printed sheet through a print fusing subsystem; and controlling print fusing operational parameters of said print fusing subsystem by analyzing said signals and automatically adjusting said operational parameters to an optimal set of parameters for the sheet.
In another aspect, the present invention provides a method for controlling hard copy apparatus subsystems printing operation parameters, via a hard copy apparatus controller, including the steps of: recognizing print medium characteristics during said medium input; recognizing said subsystems printing operation parameters current states; and based on said steps of recognizing print medium characteristics and recognizing said current states, commanding said subsystems to adjust printing operation parameters from said current states to adjusted states for optimizing print quality in accordance with said characteristics.
In another aspect, the present invention provides a hard copy apparatus, having mechanisms for electrophotographically processing image printing data as a printed page and mechanisms for controlling the mechanisms for electrophotographically processing image printing data, including printing and media transport subsystems thereof, including: connected to the mechanisms for controlling, at least one sensor for ambient environmental conditions, at least one sensor for media parameters and at least one sensor for print quality characteristics, wherein signals from each said sensor to said mechanisms for controlling are provided to said mechanisms for controlling for determining and adjusting operational parameters of said mechanisms for electrophotographically process image printing data to optimal levels for printing the image data on a media sheet passing through said apparatus.
In another aspect, the present invention provides a memory device having a program for controlling electrophotography device subsystems including: computer code enabling the recognition of signals indicative of print media characteristics, signals indicative of printed image characteristics, and signals indicative of current electrophotography device subsystems operational parameters; computer code determining optimal electrophotography device subsystems operational parameters based upon analysis of said signals indicative of print media characteristics and signals indicative of printed image characteristics; and computer code commanding adjustments to the electrophotography device subsystems operational parameters based upon the analysis of said signals indicative of print media characteristics and signals indicative of printed image characteristics.
Some of the advantages of the present invention are:
it improves control of laser printer operations in real time;
it improves fusing hard copy toner;
it improves print quality;
it provides automatic adjustments to printing processes across multiple print media types;
it provides a system where no end-user interaction is required at the hard copy apparatus due to media and environment changes;
it alleviates the necessity for print job monitoring; and
it provides data useful in determining whether maintenance processes should be implemented.
The foregoing summary and list of advantages is not intended by the inventors to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01 (d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.